Effect of indomethacin on febrile response to recombinant human interleukin 1-alpha in rabbits

Effects of indomethacin, a potent inhibitor of prostaglandin (PG) synthesis, on the fever induced by recombinant human interleukin 1-alpha (rhIL 1-alpha) was studied in conscious rabbits. Intracerebroventricularly administered rhIL 1-alpha induced a dose-dependent increase in colonic temperature that was prominently suppressed by pretreatment with indomethacin given either intracerebroventricularly or subcutaneously. On the other hand, fever induced by intravenous administration of rhIL 1-alpha was not completely suppressed by either subcutaneous or intracerebroventricular indomethacin; a small rise in colonic temperature persisted at approximately 45 min after rhIL 1-alpha injection. This rise in colonic temperature was suppressed when indomethacin was given both intracerebroventricularly and subcutaneously. It is suggested that PGs synthesized in the central nervous system contribute to the IL 1 fever and that part of IL 1-alpha given peripherally is also transmitted into the central nervous system to contribute to IL 1 fever.

Antibody to tumor necrosis factor (TNF) reduces endotoxin fever

Antibody to tumor necrosis factor (TNF), injected intravenously, reduced endotoxin fever in the rabbit. The fever-reducing effect was apparent in the latter half of the febrile response.

Regional differentiation of sympathetic nerve activity during fever caused by intracerebroventricular injection of PGE2

In urethane-anesthetized rabbits prostaglandin E2 (PGE2) injected into a lateral cerebral ventricle (icv) produced hyperthermia. During the phase of rising rectal temperature, renal sympathetic activity monitored by multi-unit recording was reduced while the drop of ear skin temperature indicated cutaneous sympathetic activation. These reciprocal changes in activity corresponded to those typical for cold stress as well as for the phase of rising body temperature in fever induced by endotoxic lipopolysaccharides (LPS). However, a slight early stimulation of the heart rate after icv PGE2, contrasted to the initial reductions seen with LPS fever and in the cold. After sino-aortic denervation renal sympathetic inhibition in response to icv PGE2 was reduced but not abolished. After cervical vagotomy the antagonism between cutaneous and visceral sympathetic activity and the increase in heart rate became more prominent. During the phase of subsiding hyperthermia after icv PGE2, renal sympathetic activity returned to its control level, but, unlike LPS fever, did not exceed it. The results of this study indicate that the reciprocal changes in cutaneous and renal sympathetic activity, but not of sympathetic outflow to the heart, are identical during the phase of rising temperature in PGE2 and LPS fever. During the phase of subsiding hyperthermia, renal sympathetic activities change to different extents in PGE2 and LPS fever.

Fever and fever syndrome--current problems

Research into the complex humoral and neurophysiological events of pyrogen-induced fever has proceeded rapidly to establish the thermal and non-thermal components of the fever syndrome. The major breakthroughs derive from the elucidation of the identity of the endogenous pyrogen interleukin 1 with the humoral factors responsible for the acute phase reaction and for the activation of lymphocytic, cellular, and immunological defence as host responses to infections. As a consequence, fever research is no longer concerned primarily with the changes in temperature regulation responsible for the febrile alteration of temperature regulation, but aims at the elucidation of the contributions that are made by both the thermal and non-thermal components of the fever syndrome to the defence of the host against the microbial intruder responsible for this syndrome. In order to account for this development in these introductory remarks to the current issues of fever research, this review has tried to pay particular attention to the following points: 1) The role of humoral factors in the generation of febrile hyperthermia, including endogenous pyrogens as well as mediators acting on the thermoregulatory center. 2) The "fever syndrome" with special consideration of its regulation and of the significance of its components from the viewpoint of fever as a host-defence reaction. 3) The assessment of the role of PG's in the generation of the fever syndrome, both as putative central mediators and as systemically released agents, with special consideration of the inhibitory action of the established antipyretic drugs on PG synthesis.

Threshold dissociation of thermoregulatory effector responses in febrile rabbits

When the core temperature stabilizes at a hyperthermic level after iv injection of lipopolysaccharide (LPS), the threshold core temperature for cutaneous vasoconstriction (Thcv) is significantly increased in hot and neutral environments, while the threshold core temperature for shivering (Thsh) is not significantly altered in hot or cold environments but is significantly reduced at thermoneutrality. This type of dissociated threshold alterations of thermoregulatory effector responses seems to be typical for the febrile response of rabbits to LPS. Because the same threshold dissociation can be demonstrated after icv injection of LPS, the systemic and the central effects of LPS in the generation of fever seem to be mediated by identical mechanisms. Prostaglandins of the E series (PGE), one of the mediators considered as important in fever generation, cause parallel increases in Thcv and Thsh when injected icv. This indicates that the mode of action of PGE on the central targets producing hyperthermia differs from that of the ensemble of mediators involved in the generation of LPS fever in rabbits. In rabbits pretreated with aspirin, the threshold dissociation after iv LPS injection still occurs. This indicates that factors other than PGE play an important role in the generation of the threshold dissociation of thermoregulatory effector responses, which is typical for LPS fever. These data indicate also that the states of activity of the thermoregulatory effectors involved in the febrile responses can be altered individually and that the activities of these effectors during LPS fever are quite different from their activities in the control state.

Hypothermia enhances acetylcholine-induced contraction of isolated rat ileum

The amplitude of acetylcholine (ACh)-induced contraction of isolated rat ileum was enhanced at medium temperatures lower than normal body temperature. Maximum enhancement was achieved between 30 and 25 degrees C. Changes in medium pH and activities of the enteric nervous system due to temperature changes were not essential for this enhancement.

Characteristics of cardiovascular responses of the bullfrog (Rana catesbeiana) to thermal stimulation of the spinal cord

Selective thermal stimulation of the spinal cord caused changes in ventricular pressure (VP) and blood flow of the pulmocutaneous artery (PCBF) in the bullfrog, Rana catesbeiana, anaesthetized with urethane. Warming the spinal cord significantly increased VP from 28.4 +/- 2.5 to 37.2 +/- 3.5 mmHg (n = 8) and PCBF from 24.5 +/- 1.4 to 29.5 +/- 2.0 ml/min (n = 5). Spinal cord cooling significantly decreased VP from 29.3 +/- 2.5 to 24.0 +/- 1.9 mmHg (n = 6) and PCBF from 22.4 +/- 1.4 to 18.5 +/- 1.7 ml/min (n = 5). Although heart rate did not exhibit significant changes during thermal stimulation, changes in cardiac output were achieved by changes in VP, i.e. changes in stroke volume. Changes in VP were antagonized with propranolol, but not influenced by lower sympathectomy which eliminates the catecholamine release for the chromaffin tissue. Atropine significantly increased resting PCBF but failed to antagonize changes in PCBF. This shows that changes in PCBF during spinal cord thermal stimulation are not mediated by an active vasomotor mechanism, but result from changes in cardiac output. The present results show that changes in spinal cord temperature induce inotropic effects on the bullfrog heart through a beta-adrenergic mechanism of sympathetic nervous origin.

Comparison of the action of prostaglandin with endotoxin on thermoregulatory response thresholds

Prostaglandin E2 (PGE2) and lipopolysaccharide (LPS) derived from E. coli were injected into the lateral cerebral ventricle of rabbits at 30 degrees C ambient temperature. The threshold core temperatures for ear cutaneous vasoconstriction (Thv) and shivering (Thsh) were determined by whole-body cooling with an intestinal thermode. Each threshold, as determined at the plateau phase of LPS fever and PGE2 hyperthermia respectively, were compared with the control values before LPS and PGE2 injection. Thsh was not changed by the injection of LPS, while Thv was increased. After PGE2 injection both Thsh and Thv were increased in comparison to their control levels. These changes paralleled the elevation of core temperature. The present study does not exclude prostaglandins as humoral mediators involved in some of the central processes generating fever, but suggest at the same time that there are additional properties of LPS fever for which prostaglandins do not account.

Cardiovascular responses of the bullfrog (Rana catesbeiana) to thermal stimulation of the spinal cord

Selective thermal stimulation of the spinal cord was performed in the bullfrog (Rana catesbeiana). Spinal cord warming caused an increase in systolic pressure of the truncus arteriosus, and cooling caused a decrease. Spinal cord warming caused an increase in systolic and pulse pressures of the conus arteriosus, and cooling caused a decrease. These results showed the temperature perceptibility of the spinal cord and a relationship between spinal cord temperature and autonomic functions in the frog as in other endothermic and ectothermic species.

Inhibitory effect of alpha-alpha-diphenyl-alpha-propoxyacetic acid-L-methyl-4-piperidyl ester hydrochloride on the activity of the rat urinary bladder

alpha-alpha- Diphenyl-alpha- propoxyacetic acid-l-methyl-4-piperidyl ester hydrochloride(propiverine) significantly decreased the volume-pressure ratio of the rat urinary bladder and suppressed efferent nervous activity of the bladder branch of the pelvic nerve during vesical extension.

Increase in oxygen consumption induced by selective spinal cord cooling in the exercising pigeon

Six domestic pigeons with chronically implanted spinal thermodes were exercised on a treadmill at neutral ambient temperature. During the exercise the spinal cord was cooled to 34.7 +/- 0.4 degrees C (mean +/- S.E.M.). Oxygen consumption of the pigeons increased from 28.3 +/- 2.1 to 61.2 +/- 3.7 ml X min-1 X kg-1 due to exercise per se, and superimposed cooling of the spinal cord during exercise induced an additional increase in oxygen consumption to 84.9 +/- 4.5 ml X min-1 X kg-1. The result demonstrates that cooling of the spinal cord elicits shivering in exercising pigeons at thermoneutral conditions.

Renal sympathetic baroreflex during normoxia and during hypoxia in conscious and in anesthetized rabbits

The responses of renal sympathetic nerve activity (RSNA) to changes in mean arterial pressure (MAP) during normoxia and hypoxia was studied in conscious rabbits and during anesthesia with pentobarbitone (PB) by determining the RSNA baroreflex curves. In conscious rabbits, the gain in RSNA response was greater and the range of MAP between minimum and maximum levels of RSNA was narrower than in anesthetized rabbits. The renal sympathetic baroreflex was augmented by hypoxia, indicating a central excitatory interaction between the effects of baro- and chemoreceptor stimulation. However, hypoxia produced no significant change in median blood pressure. During anesthesia with PB, resting MAP was decreased, median blood pressure was lowered, and renal sympathetic baroreflexes were less pronounced. Renal sympathetic baroreflex was augmented by hypoxia, and there was a significant increase in median blood pressure. These results provide direct evidence of an inhibitory effect of PB on the response of RSNA to baro- and chemoreceptor stimulation.

Renal and cutaneous vasomotor and respiratory rate adjustments to peripheral cold and warm stimuli and to bacterial endotoxin in conscious rabbits

In conscious rabbits peripheral cold stimuli decreased respiratory rate and increased cutaneous vasomotor tone while simultaneously renal sympathetic nervous discharge decreased. Peripheral warm stimuli produced the reverse pattern of autonomic effector activity. Injection of a bacterial endotoxin at warm ambient temperature elicited a biphasic fever response. Within the first 60 min cutaneous vasomotor tone increased, simultaneously renal sympathetic activity decreased. Therefore, ear skin vessels dilated and renal sympathetic activity increased by about 100%. Respiratory rate remained depressed during both fever phases. Renal blood flow was investigated in a second series of experiments and showed a negative stimulation but only in the first phase of fever. The results show that renal innervation is involved in the typical thermoregulatory autonomic activity pattern by which temperature homeostasis is preserved. The vasomotor patterns of cold and heat stress developing during fever are compatible with the concept of a changed set-point of the body thermostat. The depressed respiratory rate and the lack of the renal vascular response to the increased nervous activity during the second fever phase and their reversal to normal after acetylsalicylate (ASA) indicate the participation of prostaglandins modifying peripheral and central neurotransmitter mechanisms.

Antagonistic changes of gastric and colonic motility during selective thermal stimulation of thoracic and lumbosacral cords in anesthetized dogs

Changes in gastric and distal colonic motility evoked by thermal stimulation of the thoracic and lumbosacral cords, either individually or simultaneously, were investigated in spinal-intact dogs and in dogs spinalized at the cervical level. Simultaneous cooling of the thoracic and lumbosacral cords increased both gastric and colonic motility before and after spinalization. The direction of the responses evoked by simultaneous heating was the opposite, but only the decrease in gastric activity in the spinal-intact dog was significant. Selective cooling of the thoracic cord increased gastric motility, but decreased colonic motility before and after spinalization. Selective heating decreased gastric motility before and after spinalization, and increased colonic motility before spinalization. Selective cooling of the lumbosacral cord decreased gastric motility and increased colonic motility in spinal-intact dogs. No significant responses could be observed during selective heating in spinal-intact dogs. However, in spinalized dogs, the selective cooling and heating increased and decreased colonic motility respectively, while no significant change was observed in gastric motility during the cooling and the heating. It is concluded from the results that thermal stimulation of the spinal cord directly affects spinal functions which control gastrointestinal motility, and that there exists a mutual inhibitory interaction between the thoracic and lumbosacral innervation of the gastrointestinal tract.